This invention relates to a method of inspecting a die for forming honeycomb structures, and more particularly to a method of inspecting a die for forming honeycomb structures, which is able to precisely inspect worked conditions of inner surfaces in a great many rear apertures for supplying ceramic batches into the die.
Ceramic honeycomb structures have been widely used as catalyst carriers for purifying exhaust gases of automobiles. Such ceramic honeycomb structures are generally formed by extruding ceramic batches through a honeycomb forming die having slits of narrow widths of the order of 0.1-0.2 mm and a great number (as much as thousands) of rear apertures communicating with the slits for supplying the ceramic batches.
It is of course that quality of formed honeycomb structures is directly affected by configurations and dimensional accuracy of the slits of such honeycomb forming dies. In addition, since flowing resistance of ceramic batches passing through rear apertures of the die is affected by roughnesses of inner surfaces of the rear apertures for supplying the ceramic batches, it is needed to work the rear apertures so as to obtain uniform inner surface roughnesses in order to prevent malformed honeycomb structures. However, these rear apertures are great in number and very deep relative to their diameters so that a surface roughness tester cannot be used for measuring surface roughness on inner surfaces of the rear apertures. There has been no suitable inspecting method for this purpose. Therefore, when a new honeycomb forming die is used, it is unavoidable that the die is set in an extruding machine and honeycomb structures are actually formed whose defects are used for determining whether roughnesses of the rear apertures of the die fulfill the requirement or not. Such a judgment requires troublesome and time-consuming operations and gives rise to confusions in a production shop.